Gigabit-Capable Passive Optical Network (GPON) technology is a passive optical access technology applying a point-to-multipoint topology structure. The topology structure of the GPON system is shown in FIG. 1, wherein, the GPON comprises Optical Line Terminal (OLT) at the central office, Optical Network Units (ONUs) at the end user and an Optical Distribute Network (ODN), and a point-to-multipoint network structure is usually used. The ODN comprises single-mode optical fibers, optical splitters, optical connectors and other passive optical components, and the ODN provides optical transmission medium for the physical connection between the OLT and the ONUs.
To date, a downlink rate of 2.5 Gbit/s and an upstream rate of 1.25 Gbit/s are widely used in the GPON. With the development of communication technologies such as the Internet, the number of users accessing to the Passive Optical Network (PON) system is gradually increasing, so is the demand by the users for bandwidth, therefore, the next-generation PON technology based on the GPON technology has experienced rapid development and it is XG PON technology whose downlink rate is 10 Gbit/s and upstream rate is 2.5 Gbit/s (or 10 Gbit/s). Since the ratio of downlink rate to upstream rate in the traditional GPON technology is 2:1, based on this model, operators now proposed the rate demand that the next-generation PON technology is XG PON whose downlink rate is 10 Gbit/s and upstream rate is 5 Gbit/s (10 Gbit/s). To meet the need for upstream rate of 5 Gbit/s, in the prior art, it is proposed to use two 2.5 Gbit/s optical modules with different wavelengths to achieve the 5 Gbit/s upstream rate, however, this technique requires that the media access control chip in the OLT has two pairs of differential lines for receiving upstream data, which occupies hardware pin resources and is not conducive to the network upgrade and expansion, and the valuable wavelength resources are wasted. Another technique proposes to use double binary code technique to enable the optical module with a transmission rate of 2.5 Gbit/s to send data of 5 Gbit/s, but this technique requires using special modulation techniques, which greatly increases the cost of the ONUs, and a plurality of optical power budgets are lost in the upstream optical link in the PON system, which deteriorates the performance of the upstream optical link.